Track circuit for railroads



Nov. s, 1938.

W. H. REICHARD TRACK CIRCUIT FOR RAILROADS 7 Filed May 26, 1934 IINVE TOw. A

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"44m fl ATTORNEY Patented Nov. 8, 1938 PATENT OFFICE TRACK CIRCUIT FORRAILROADS" Wade H. Rei'chard, Rochester, N. Y., assignor to GeneralRailway Signal Company, Rochester,

Application May 26,. 1934,. Serial No.. 727,691.

11' Claims.-

This invention relates in general. to track. circuits such asusedinrailway signaling practice and has more particular referencetomeans.for.

automatically. discriminating between current. changes in :the, trackcircuit due. tothe. occupied condition' of. the track anddue. to.leakage. currents resulting frompoor ballast conditions.

In railway operation it is quite. essential that the. usual track relayconnectedacross the track 1 sectionat. oneend of: a. signaling block besufliciently energized when the block is unoccupied. to. pick upandholdup with certainty. It-is likewise essential that the. occupancy. ofthe track section will so effectively shunt. or condition. the relaythat it will bepositivelyreleased. For ex-' ample, in the usual trackcircuitsif the normal holding currenttis. too-high, shunting may notbe.- effective todrop the. relay and if the normal hold--- ing currentis so lowthat shunting will be more positive it is. possible that attimestheholding current may. be insumcient.

Taking theabove intoiconsideration it will beseen that the usualvariation -in ballast resistance encounteredin practice, .dueprimarilytochanges in weather conditions, may operate to interfere with theproper operation of the track relay unless some means is provided fordiscriminating between changes due to ballast resistance and trackoccupancy.

Asthe ballast resistance. increases, the leakage current between therails. decreases so that the voltage across the terminals of the. trackrelay connected to the track circuit increases; Con-- versely, astherballast resistance decreases, ballast leakage increasesand theterminal voltageat the relay decreases.

The relay current will vary over a considerable range and cover a rangeat times which will prevent proper response of the relay under occupiedv or unoccupied conditions of'the track section.

It is proposed in accordance with this invention to-provide means,associated. with. the track relay for discriminating or detecting achange due to track occupancy and. unoccupancy' and.

changes due to leakage currents caused by variation in ballastresistance between thelrails ofv the: track. In accordance. with: thepresent invention it is proposed to improve theshunting efiiciency'of'the trackcircuit and for this purpose. a; discriminating arrangement'is included-in thecircuit of the track relay which discriminates be-'tween a slow change intrack. shunt due to track ballast and'a rapidchange in. track shuntdueto train occupancy.

Further objects, purposes and. characteristic featuresof. theinventionwill appear as the description progresses, reference. being made to theaccompanying. drawing showing by way of example-.oneform. which theinvention may assume.

The. ingle figure diagrammatically illustrates 5 one form of the presentinvention applied to a singlestretch of track.

Apparatus-Referring tothe drawing, a section of railway track includingrails l is shown separated from; the adjacent track sections by 10insulated jointsZ. Atrackbattery IB and a limiting resistance R. areshown connected to the trackrails atthe right-hand end of theillustrated track section.

As. typical-of-the control exercised by the track relay, asemaphoresignal SG is illustrated at the left handend-of the. track section. Atrack relay T, havingtwocoils is illustrated, the control of which willbe. explained in detail. A Pliotron or amplifier: tube R0 of any wellknown type is used, and as illustrated, is adaptedto control, by meansof. the voltage generated in the secondary of transformer TR, thecurrent for operating selecting relay. IS.

Associated withPliotron RC is theusual plate source of current which maybe, a battery 2B andthe usual filament.- source: of current which may beabattery A; Bias. resistor BR is adjustably connected to thegrid.circuit of the amplifier in order toprovide a normal biasto the in-putof theetube-for. a purpose that will .be later. described. Slowactingselecting relays2S and 38 are provided and these relays incooperation with relay IS-insertresistances IR, 2Rand BB. in the trackcircuit under certain conditions-in a manner and for a purpose that.will be explained in detail.

Normal conditions.-With the circuit in its normalicondition asillustrated in the figure, track relay T is normally picked up over acircuit extendingfromthe terminal of battery lB, resistance R, lowertrack. rail; lower winding and upper winding of relay T in series,primary winding of transformer TR,.front contacts ll, l2 and i3 ofrelays. IS, 28 and 3S respectively and upper track rail to the terminalofbattery IB. The constants.of.the described energizing circuit forrelay Tareof such'a value that suflicient current flowsunder the worstballast conditions (maximumleakage betweenv track rails) to maintain thecontacts oi'relay T' picked up. The best ballast conditions. (minimumleakage between track rails) allows more. current toflow over the abovedescribed circuit including relay T which of course willmaint'ain.its-contactsin their picked up. positions.

Any change in current flow over the above described circuit takes placethrough the primary winding of transformer TR but such a change due to achange in ballast conditions takes: place quite slowly, so that there isno appreciable effect on the secondary winding of transformer TR due tosuch a change.

Adjustable bias resistor BB is so adjusted that the grid of amplifier RCis normally sufficiently positive with respect to the filament thatsurficient current flows from the terminal of battery 2B, winding ofrelay IS, plate filament circuit of the amplifier and resistor BR to theterminal of battery 23, for maintaining relay IS in its picked upcondition. Since slow changes in the track circuit current flow have noapp eciable effect on the grid circuit of amplifier RC, this bias ismaintained substantially constant so that relay IS is not affected bysuch changes.

Relay 2S is normally energized over a circuit extending from frontcontact I4 of relay IS and winding of relay 28, to Relay 3S is normallyenergized over a circuit extending from front contact I of relay 2S andwinding of relay 38, to 'With relays IS, 2S and 3S picked up,resistances IR, 2R and 3R are short circuited at front contacts II, I2and I3 so that they are not included in the circuit of the track relay.

Track occupancy.When the illustratedtrack section is occupied the shuntacross thetrack rails, due to the wheelsand axles of the train, causes asudden decrease in the current flowing through the windings of relay'1'. This sudden decrease inthe current flow through the circuitincluding the primary winding of transformer TR, which is in series withthe track relay windings, sets up a potential across the secondaryWinding of transformer TR in such a direction that the terminalconnected to the grid of amplifier RC' becomes more negative withrespect to the filament to such an extent that the current flow throughthe plate circuit of the amplifier is reduced to a value which causesrelay IS to drop its contacts. Even though this potential is onlymomentary, relay IS has time to drop its contact-s and after the gridcircuit returns to its normal state, with normal current flowing throughthe plate circuit of the vacuum tube, this current is insufiicient topick up relay IS after it has dropped its contacts. This is due to thefact that the pick up current'for the relay is considerably higher thanits holding current.

The dropping of front contact II removes; the shunt from resistor IR sothat this resistor is inserted in the circuit. of relay T. This furtherreduces the currentcfiow through the windings, of

relay T so that'it has less holding power than when the track rails wereshunted by the train. Relay T may or may not release underthiscondition. If it does not release within a predetermined time, relay2S will drop its contacts because front contact I4 of relay lSdeenergizes the winding of relay 2S. Relay 2S inserts resistance 2R inthe circuitincluding relay T, by dropping its front contact I2. Relay'1' may or may not release under this condition. If it does not releaseafter 'a predetermined interval of time, crelay SS is dropped becauseits energizing circuit is open at front contact I5 of relay 2S; .Relay3Sthen inserts resistance 3R in the track relay circuit by dropping itsfront contact I3.

. It will be understood that additional selecting relays may be providedif required, or if 1 ,condi tions are such that only one resistorIR needbe track relay circuits.

lay Ta stick circuit is provided topreve'nt other selector relays beingdropped, which circuit extends from back contact I 5 of relay T, frontcontact I! and winding of relay 2S, to The stick circuit is alsoefiective to stick relay 3S over a'circuit including its front contactI8 and its winding, to

It will thus be observed that relays IS, 28 and 3S function tosequentially insert resistance in the circuit of the track relay untilit releases, after which those relays (if any) which were not releasedwill be stuck up through a back contact of the track relay.i Since thestick circuits of the 2S and 3S relays are opened at their own frontcontacts, after the track relay is dropped I the selector relays are notagainpicked up until the track becomes unoccupied as will be described.

Contact 2| of relay T and contact 3I of relay IS in series may be usedto control the signal circuits of signal SG or for any other purposerequired by the usual practice in connection with Front contact 22 ofrelay SS is not shown connected to any circuit but this contact isincluded to indicate that another selecting relay can be provided whendesired and connected to front contact 22 of relay 3S in a similarmanner to. which relay 3S is connected to front contact I5 of relay 2S.I

Track 'unoccupcmcu-When' the train leaves the track section, the quickremoval of the shunt across the'track railscauses a sudden increase incurrent flow through the track circuit including the primary winding oftransformer TR andthe windings of the track relay in series, This suddenincrease in current flow sets up a potential across the secondarywinding of the transformer in an opposite sense to thatpreviouslyexplained so that the grid of amplifier RC 7 7 positive with respecttothe filament. This'positive potential on the grid'permits sufii'cientcurrent to flow through the plate filament, circuit for picking up relayIS. Relay IS removes resistor IR from the track circuit and closes acircuit at its front contact I4 for picking up relay.

2S. Relay 2S removes resistor 2R from the track circuit and closes acircuit at its front contact I5 for picking up relay is. Relay 3Sremovesresistor 3R from the track circuit. It will be understood that in theevent that'relay 3S or 28 were not dropped under the previous condition,then' when the track becomes unoccupied relay IS will pick up to removeresistor IR which under this conditionis the only one included. 7 Withrelays IS, 2S and 3S picked up, the circuits are in condition formaximum current flow becomes more' through the windings of relay T whichcauses this relay to be picked up; The circuits are now in normalcondition.

It will be clear from the above description that this invention providesmeans whereby there is a' a positive discrimination between the trackcircuit conditions due to track occupancy and due to ballast leakage. sr

The above rather specific description of one form of the presentinvention has been given solely by way of illustration and is notintended 1. "In 'aitrack circuit, an insulated section or track, 'asource of current connected to said track, a track relay "connected tosaid track and energized in slowly varying degrees in accordance withthe slowly changing current values due to variations in ballastresistance, the entrance of a train into said section of track producinga'rapid reduction in the current in the circuit of said relay, and meansresponsive only to said rapid reduction of current forsequentially-inserting resistance units in the circuit of said relayuntil the resistance of the circuit including said relay has increasedto a value where said relay releases.

2. In a track circuit, in combination with an insulated stretch oftrack, a source of current connected across one end of said track, atrack relay connected across the other end of said track, an energizingcircuit for said track relay including the track rails, a thermionicdevice, a transformer having its primary winding connected in serieswith said track relay and its secondary winding connected to the in-putcircuit of said thermionic device, a control relay connected in theout-put circuit of said thermionic device, the resistance voltage dropacross a portion of said energizing circuit supplying the in-put circuitof said thermionic device with a normal bias which maintains saidcontrol relay picked up irrespective of changes in the ballast conditionof said stretch of track, and the voltage induced in the secondarywinding of said transformer due to the entrance of a train into saidstretch of track being sufficient to overcome said bias to cause saidcontrol relay to release, and means responsive to the release of saidcontrol relay for effecting a control of said track relay.

3. In a track circuit, in combination with an insulated stretch oftrack, a source of current connected across one end of said track, atrack relay connected across the other end of said track, an energizingcircuit for said track relay including the track rails, a thermionicdevice, a transformer having its primary winding connected in serieswith said relay and its secondary winding connected to the in-putcircuit of said thermionic device, a control relay connected in theout-put circuit of said thermionic device, the resistance voltage dropacross a portion of said energizing circuit supplying the in-put circuitof said thermionic device with a normal bias which maintains saidcontrol relay picked up irrespective of changes in the ballast conditionof said stretch of track, the voltage induced in the secondary windingof said transformer due to the entrance of 'a train into said stretch oftrack sufficiently changing said bias to cause said control relay torelease, and means controlled by said control relay for graduallyinserting resist ance in said track circuit until and only until saidtrack relay is released.

4. In a track circuit, in combination with an insulated stretch oftrack, a source of current connected across one end of said track, atrack relay connected across the other end of said track, an energizingcircuit for said track relay including the track rails, a thermionicdevice, a transformer having its primary winding connected in serieswith said relay and its secondary winding connected to the in-putcircuit of said thermionic device, a control relay connected to theout-put circuit of said thermionic device, the resistance voltage dropacross a portion of amass-o said -energizing circuit supplying the'in-put circuit-of said thermionic device with alnormal bias whichmaintains said control relay picked up irrespective of changes in =theballast condition of said stretch of track, the voltage induced in thesecondary winding of said-transformer due to the entrance of a traininto said stretch of track sufliciently' changing said bias to causesaid control relay *to release, means controlled by said 'control relayfor gradually inserting resistance in said track circuit until and onlyuntil said track relayis released, and means controlled by the exit ofthe -tr'ain*'fromsaidstretch of track for sufliciently changing saidbias to cause said control relay to pick up.

5. A track circuit comprising an insulated track section; a track relay;a resistance normally excluded from the circuit of said track relay;discriminating means including a thermionic relay; means responsive tothe occupancy of said section for operating said discriminating means;means responsive to the operation of said discriminating means forincluding said resistance in the circuit of said track relay; and meanscontrolled by said track relay for controlling the amount of resistanceincluded in its circuit.

6. In a track circuit, an insulated section of track, a source ofcurrent and a track relay connected to said track, a plurality ofresistance units, slow-acting means for slowly and sequentiallyinserting said resistance units in series with said track relay until itreleases, means in cluding an impulse actuated device for starting theoperation of said slow-acting means, and means controlled by the releaseof said track relay for stopping the operation of said slow-actingmeans.

7. In combination, a section of railway track, a source of currentconnected across the rails of said section, a relay receiving energyfrom the rails of said section and responsive to the steady value ofcurrent with which it is supplied, a transformer also receiving energyfrom the rails of said section, and means energized from saidtransformer and responsive to a change in the energization of thetransformer occurring upon the entrance of a train into said section fordecreasing the energization of said relay whereby said relay willrelease.

8. In combination, a section of railway track, a source of currentconnected across the rails of said section, a relay receiving energyfrom the rails of said section and responsive to the steady value ofcurrent with which it is supplied, a transformer having a windingincluded in the energizing circuit for said relay, and means energizedfrom a winding of said transformer and responsive to a change in theenergization of the transformer occurring upon the entrance of a traininto said section for decreasing the energization of said relay wherebysaid relay will release.

9. In a track circuit for railroads, the combination with a section ofrailway track having a track relay and a source of uni-directionalcurrent connected thereto, an auxiliary relay separate from said trackrelay and effective when operated to decrease the current through saidtrack relay and thereby cause release of its armature, and meansincluding a transformer for causing operation of said auxiliary relay inresponse to the relatively quick change in the current in said trackcircuit caused by the entrance of a train into said section.

said section, a first relay receiving energy from the rails of saidsection and responsive to the steady value of current with which it issupplied, V I

a second relay, means for controlling said second relay in accordancewith the-rate of change of current fiow'in said first relay when thevalue,

of current through said first relay is quickly decreased due to theentrance of a train into said section, and means controlled by saidsecond relay for decreasing the energization of said 10 first relay. 7 s

WAD E BEI CI-IARDL

